Orthodontic therapy is a specialized type of treatment within the field of dental treatment, which involves movement of malpositioned teeth to functionally improved and correct locations. Orthodontic treatment often improves the patient's occlusion (i.e. bite) and typically enhances the aesthetic appearance of the teeth.
Many types of fixed orthodontic treatment programs involve the use of a set of tiny devices known as brackets and wires that are collectively known as “braces”.
Most orthodontic brackets have archwire slots that are open on one side for insertion of the archwire. The typical location of the archwire slot is horizontal, and runs from a mesial to distal location. The wire is inserted from the buccal/labial (i.e., cheek/lip side, referred to sometimes in the art as the “facial” side) to the lingual (i.e., tongue side) direction. The wire is bounded on occlusal (i.e., the side facing the tips of the patient's teeth) and gingival (i.e., the side facing the patient's gingiva or gums) sides by walls or functionally similar structures.
Many orthodontists use ligatures to secure or engage the archwire in the archwire slot. One type of commercially available orthodontic ligature is a small, elastomeric O-ring. Orthodontic O-rings are stretched around small wings (known as “tiewings”) that are connected to the bracket body on the gingival side and on the occlusal side of the archwire slot. Once installed, the O-ring ligature extends around the tiewings as well as over the buccal-labial surface of the archwire and exerts pressure on the archwire to reach a fully seated position in contact with a lingual wall of the archwire slot.
Stainless steel ligatures are alternatively used to retain archwires in archwire slots of brackets. The metal ligature is hooked around the tiewings and extended over the labial side of the archwire. End sections of the ligature are then twisted together, and pulled tight to form a loop to retain the archwire in place.
Elastomeric ligatures can suffer from force decay and staining, while metal ligatures often have sharp ends that may retain food, irritate cheek and gum tissue, and increase the risk of infection caused by puncture of an operators tissue through a glove-covered hand.
To solve some of the above mentioned ligation problems, a variety of orthodontic brackets have been proposed having various types of clips or latches for securing the archwire in the bracket. These brackets are commonly known as self-ligating brackets. The latch comprises a clip, spring member, cover, shutter, bail or other structure that is connected to the bracket body for retaining an archwire in the archwire slot. This type of self-ligating securing technique potentially eliminates the need for elastomeric or metal ligatures to secure the archwire. As a result, the time required to secure an archwire or replace an archwire in a self-ligating system is dramatically reduced.
Examples of self-ligating orthodontic brackets having U-shaped ligating latch clips are described in U.S. Pat. Nos. 3,772,787, 4,248,588 and 4,492,573. In general, the clip of such a U-shaped bracket is opened by pushing the latch to an open position with a small-tipped dental instrument. Another example is the Speed™ self-ligating bracket, which has a movable generally U-shaped clip for retaining the archwire.
Examples of self-ligating orthodontic brackets having c-shaped shutters are described in U.S. Pat. No. 6,582,226. Examples of orthodontic brackets with swinging latches are described in U.S. Pat. Nos. 4,103,423, 5,516,284 and 5,685,711.
U.S. Pat. No. 5,711,666 discloses a self-ligating bracket with a latch that comprises a flexible flat spring member. One end of the spring member is fixed to the bracket body on one side of the archwire slot, and the opposite end of the spring member has notches that releasably engage latch sears or catches when the spring member is moved to a slot-closed position. To open the slot, the notches are disengaged from the catches and the spring member is bent to an orientation sufficient to enable the archwire to be removed from the archwire slot.
Other types of self-ligating orthodontic brackets have latches that comprise essentially flat plates that are slidable between a slot-open and a slot-closed position. Examples of such brackets are shown in U.S. Pat. Nos. 5,094,614, 5,322,435 and 5,613,850. In general, the sliding latches described in these references move in upright channels that are located buccolabially of the archwire slot.
Another type of self-ligating bracket that has been proposed in the past has a latch that is made of a section of wire material that functions similar to a bail. The orthodontic brackets described in U.S. Pat. Nos. 4,149,314, 4,725,229 and 5,269,681 have wire-like latches that swing between a slot-closed position and a slot-open position. The orthodontic bracket described in U.S. Pat. No. 4,260,375 has a wire latch that is slidable between a slot-open and a slot-closed position.
In general, there are three types of tooth movement that are important to orthodontic practitioners. Rotational movement, as its name suggests, is rotational movement of a tooth about its long axis. Tipping movement is another type, where the movement is primarily of the clinical crown, with minimal movement of the root tip. A third type is torquing movement, which can be defined as pivotal movement of the long axis of a tooth in a buccal-lingual direction. Preferably, the appliances selected by the practitioner for use provide precise control over movement of the associated teeth for each type of tooth movement. During the course of treatment, it may be necessary to shift each tooth relative to adjacent teeth in order to provide an aesthetically pleasing result at the conclusion of treatment.
However, known self-ligating orthodontic brackets are not entirely satisfactory because optimal control over torquing movement as described above is often difficult to achieve. Precise control over movement of the teeth is desirable so that each tooth can be shifted as needed to its ideal occlusal orientation. Furthermore, it is desirable that this be done with a minimum of friction on the archwire.
Another problem that has been noted in connection with conventional direct-bonded appliances, including self-ligating brackets, is the possibility that such brackets may spontaneously debond from the patient's tooth when the teeth are severely maloccluded. When the teeth are severely maloccluded or excessive torque is applied, for example, if one of the patient's teeth is located a relatively large distance in a lingual direction relative to adjacent teeth in the dental arch, the archwire must be deformed a significant distance in order to be engaged in the archwire slot. In such instances, the inherent tendency of the archwire to return to its normal arch-shaped configuration may cause the archwire to exert a substantial force and/or torque on the appliance bonded to the severely maloccluded tooth. Unfortunately, the bracket may then debond from the tooth if the archwire exerts a force that is larger than the force required to debond the bracket.
Brackets that spontaneously debond from teeth represent a waste of time and expense for both the practitioner and the patient, and are best avoided if at all possible.
While many types of self-ligating orthodontic appliances have been proposed in the past, there remains a continuing need to improve the state of the art of self-ligating systems. For example, it would be desirable to provide a self-ligating appliance that reduces the time needed for installation of an archwire in comparison to existing self-ligating brackets, so that the time of both the practitioner as well as the patient to complete the installation procedure can be reduced. Commercially available self-ligating systems feature an archwire slot oriented horizontally generally parallel to the occlusal plane. Most of these devices have self-ligating mechanisms, such as latches or hinges, that open and lock in a vertical or horizontal direction to the occlusal plane. Most clip and hinge devices currently commercially available have proven to be difficult to open in the posterior region of the mouth. This is due to the limited working space available between the patients' cheeks and the buccally-oriented entrance of archwire slot. Most of these devices require specially designed instruments or tools to insert the archwire and close the latch or hinge, securing the archwire in the horizontal slot. Other self-ligating systems require a special tool to pry the archwire from the archwire slot releasing it from the horizontal archwire slot of each bracket. Moreover, it would be desirable if such an appliance could provide more precise control over movement of the associated tooth by fully seating finishing archwires in the archwire slot while also facilitating gradual movement of the tooth to its desired ultimate location.
A particular disadvantage of the edgewise bracket self-ligating systems such as those described above is that they lack in truly efficient torque control. Prior art systems are either completely passive (where archwires are never fully seated in the archwire slot), or passive with small-diameter wires and only partially active when full-dimension wires are inserted into the archwire slot and the slot cover engages the inner walls of the slot more efficiently. As a result, prior art self-ligating appliances generally only achieve full-seating and thereby truly efficient torque expression through additional adjustments made to the archwire by the clinician.
U.S. Pat. No. 6,582,226 discloses a number of orthodontic brackets/buccal tubes, each having an archwire slot running across the body in a generally mesial-distal direction with a slot opening in a generally labio-lingual (horizontal) direction. A shutter retains an archwire in the archwire slot. In each of the embodiments shown, the shutter is sufficiently resilient to enable an archwire to be pushed into the slot by a user, while retaining the archwire within the slot until a predetermined minimum force applied by the archwire against the shutter is exceeded. However, the configurations shown are limited to edgewise (i.e., horizontal) bracket systems. They are further limited, by their configuration, to require selection of smaller-diameter wires throughout the entire system, as a larger diameter wire would not be held effectively by the shutter in the case of a severe malocclusion. Furthermore, control and expression of forces, particularly torque, is limited because the configurations only express torque efficiently when a full-sized finishing archwire is in place.